A rectifier is a device used to convert the electrical supply provided by a utility company in alternating current form (AC) into the direct current form (DC) that is needed by some applications. Electronic rectifiers are used in most AC/DC power supplies, motor drives (variable frequency or servo), battery chargers, etc. Almost all electronic devices powered by an electrical distribution network use a rectifier. There are many types of rectifiers from simple to complex ones, each offering difference levels of performance.
Typically, the simplest rectifiers use a number of diodes. These diode rectifiers have the characteristic of producing a significant level of current distortion, which is unacceptable for some applications, such as those that are subject to regulations or standards such as IEEE 519.
Active rectifiers have been developed in order to achieve better levels of current distortion than diode rectifiers. Traditionally, the goal has been to significantly reduce distortion beyond the limits set out by regulations and standards. Active rectifiers are more complex than diode rectifiers, and use active switches (typically transistors) to control the flow of current. However, active rectifiers have an associated cost that is higher than a diode rectifier, since the transistors used must be capable of conducting relatively high current, which makes them expensive.
Furthermore, active rectifiers typically have low efficiency at partial loads, due to the continual switching of the transistors, which produces losses even when the load goes to zero. For some applications and industries, the efficiency of known active rectifiers is unacceptably low, or, at the very least, represents a substantial problem.